Electrical indicating circuits

ABSTRACT

Lamp monitoring and failure indicating circuits are described which employ normally non-conducting semiconductor switches. The circuit potential sensed across a resistor connected to the monitored lamp biases a transistor OFF, holding a second transistor OFF. Thus in normal operation of the lamp the circuit draws no current. A fault turns both transistors ON.

United States Patent [19 Bial et al. 1 Nov. 20, 1973 ELECTRICALINDICATING CIRCUITS 3,408,625 10/1968 Skinner 340/251 [76] Inventors-Wolfgang Bial 40s Shenle Rd H969 Akmsm y 3,660,813 5 1972 Rumpf 340/251Borehamwood; Michael John McDonnell, 35 Pinner Park Gardens, NorthHarrow; Gordon Primary Examiner-Thomas B. Habecker Alan g, 3 wroxhamMansions, Att0mey-Warren, Rubin, Brucker and Chickering 36 CanfieldGardens, London, all of England [22] Filed: Mar. 24, 1972 57 ABSTRACT[21] Appl. Nov: 237,810

Lamp momtorlng and fallure mdlcatmg clrcults are described which employnormally non-conducting U-S- semiconductor switches The circuitpotential sensed [5 In Clacross a resistor conngcted to the monitoredlamp of Search a e a tran i tor a econd transistor OFF. Thus in normaloperation of the lamp the circuit References Cited draws no current. Afault turns bothtransistors ON.

UNITED STATES PATENTS 3,252,157 5/1966 Pabst 340/251 10 Claims, 3Drawing Figures ELECTRICAL INDICATING CIRCUITS The invention includeselectrical circuits for providing an indication of failure of one ormore lamps. Although the invention is not so restricted, it will bedescribed with reference to a motor vehicle lamp failure warning system;another example is in the field of lamp failure warning systems inautomated process or machinery control panels.

According to the invention an electrical circuit which provides anindication of failure of one or more lamps includes one or moreresistive elements connected respectively in series with the or eachlamp, first normally non-conductive semiconductor switch means arrangedto be biased conductive by the potential developed at the junction ofany lamp and its associated resistive element following failure of thatlamp, and second normally non-conductive semiconductor switch meansarranged to be biased conductive and to operate an electrical indicatingdevice whenever the first said switch means conducts.

Thus, circuits according to the invention may be used to monitor thecontinuity of operation of lamps, e.g. brake lights, in a motor car andto provide a visual indication upon failure of one or more of them.

Preferred embodiments of electrical circuits in accordance with theinvention will now be described by way of example with reference to theaccompanying drawings'in which:

FIG. 1 is a circuit diagram illustrating the electrical circuitaccording to the invention; and

FIGS. 2 and 3 are circuit diagrams illustrating modified versions of thecircuit of FIG. 1.

In FIG. 1 the positive and negative terminals ofa bat tery are connectedto the supply lines 11 and 12 respectively of the circuit. Wiringresistance between the battery 10 and circuit is indicated by a resistor13 and circuit protection, in the form of a fuse 14, is also provided.The two lamps to be monitored, which may be vehicle brake lamps, arereferenced 15A and 15B and are connected in series with resistors 16Aand 16B and manually operable lamp switches 17A and 17B, respectively,extending between the lines 11 and 12. The

junctions of the. lamps 15A and 15B and their individually associatedresistors 16A and 16B are connected through respective diodes 18A and1813 to the emitter of a p-n-p transistor 19, forming an AND circuit.The collector of transistor 19 is connected to line 12 via a pair ofseries-connected resistors 20 and 21. The base of transistor 19 isconnected to line 12 by a resistor 22 and to line 11 by a pair ofseries-connected diodes 23 and 24, as shown. The two diodes 23 and 24are included in the circuit to balance the forward voltage drop acrossthe diodes 18A and 18B and the emitter base junction of transistor 19.

An n-p-n transistor 25 is provided in the circuit with its baseconnected to the junction of resistors 20 and 21, its emitter coupleddirectly to line 12 and its collector connected to line 11 via anindicating lamp 26 and a lamp-protecting resistor 27.. When the switches17A and 17B are both open and the filaments of the lamps 15A and 15B aresound, the potential at each anode of the diodes 18A and 18B issubstantially the potential of line 12. Thus the transistor 19 is biasedOFF. 1f one or both of the switches 17A, 17B is or are closed, thepotential at the anodes of the diodes 18A or 188 will rise to a valuedeterminedby the potential drop across the resistors 16A, 168. Thevalues of resistors 16A, 16B are chosen such that transistor 19 ismaintained OFF. If one of the lamps, 15A say, should fail, the potentialat the anode of the associated diode 18A will rise until this diode isforwardly biased and transistor 19 turns ON. Once transistor 19 is ON,current is drawn from the line 11 via resistors 16A or 16B and diodes18A or 188 and is passed to the collector of this transistor. Thecurrent flowing through the resistors 20 and 21 will raise the potentialon the base oftransistor 25 from that of the line 12 and the resistancevalues of resistors 20 and 21 are chosen such that transistor 25 turnsON and illuminates the lamp 26. i

It has beenfound that the potential drop required across the resistors16A, 16B is, when the circuit is implemented using commerciallyavailable components, of the order of to 300 millivolts. This may be adisadvantage when, for example, the supply voltage is low and thepotential drop across resistors 16A, 16B may be a substantial proportionof the total available voltage.

An advantage of the modified forms of the circuit shown in FIGS. 2 and 3is that each is arranged such that the resistance value of the resistorsin series with the monitored lamps may be substantially reduced. Thoseof the components of the circuit illustrated in FIG. 2 which correspondsto the components shown in FIG. 1 are given the same reference numerals.

The junction of the lamps 15A, 15B and resistors 16A, 16B are in theircircuit arrangement coupled directly to respective ones of the emittersof a multiemitter transistor 30, the base of which is biased from apotential divider including a single diode, 31 and the resistor 22. Theemitter-base junctions of the transistor 30 perform the blockingfunction of the diodes 18A, 18B used previously.

The operation of the circuit shown in FIG. 2 is essentially the same asthat previously described; failure of either lamp 15A, 158 will raisethe potential at one of the emitters of transistor 30, turning thistransistor ON. The collector current of transistor 30 will generate apotential on the base of transistor 25 turning this transistor ON andilluminating the lamp 26.

It will be appreciated that the omission of the diodes 18A, 18B and thereplacement of the diodes 23 and 24 by a single diode 31 reduces thedifficulty in matching the forward potential drops across them. It hasbeen found that the potential drop required across resistors 16A, 168when the circuit of FIG. 2 is implemented using integrated circuittechnology is less than 100 millivolts, and may be as low as 50millivolts, as a result of the automatic matching of the diodeparameters in a chip".

A feature of the two circuits so far described is that the indication oflamp failure is provided only whilst the corresponding switches 17A, 17Bare closed. The modified circuit illustrated in FIG. 3 shows one way ofstaticising" or rendering permanent the failure indication.

In the circuit of FIG. 3 the lamps to be monitored include a first pairof lamps 33A and 338 connected serially, as shown, torespectiveresistors 34A and 34B. These two lamps are controlled by asingle switch 35, which may be for examle a road vehicle brake lightswitch. A second switch 36 passes current through a resistor 37 to oneor other of two lamps 38A and 3813 in dependence on the setting of atwo-way switch 39, for example, a head lamp dipping switch.

The junctions of lamps 33A and 338 with the resistors 34A and 34Brespectively are directly coupled to the emitters of two p-n-ptransistors 40A and 108. The junction of resistor 37 and the switch areaof switch 39 is similarly directly coupled to the emitter of p-n-ptransistor 40C. The base potentials of the three transistors 40A, 40Band 40C are provided by potential divider circuits formed, respectively,by diodes 41A, 41B, and 41C, and resistors 42A, 42B, and 42C,respectively, as shown. The collectors of the three transistors 40A, 40Band 40C are connected through diodes 43, forming an AND circuit to acommon line 44 which includes a potential divider formed by resistors 45and 46. The junction of these two resistors is connected to the controlelectrode of a low current silicon-controlled rectifier (S.C.R.) 47 theanode of which is connected to line 111 via two lamps 48. The cathode ofS.C.R. 47 is connected to line 12 via a resistor 49 which is shunted bya series circuit including a resistor 50, a diode 51 and an electrolyticcell 52. A capacitor 53 is coupled across the resistor 46 as shown.

In operation, failure of either lamp 33A, 338 will raise the emitterpotential of the respective transistor 40A, 408 or 40C turning it ON.The collector of the conducting transistor will pass current to line 44and generate a potential across resistor 46. This potential is arrangedto turn S.C.R. 47 ON. When S.C.R. 47 conducts, it illuminates the lamps48 and develops a potential across resistor 49. Thus the circuitincluding the electrolytic cell 52 will draw current and the state ofcharge of the cell 52 will indicate the period of time during which thewarning lamps 48 have been lit.

Similarly, if either of the lamps 38A and 38B fail while switch 39closes their circuit connection, then transistor 40C will turn ON andinitiate operation of the S.C.R. 47.

The capacitor 53 is provided to shunt high frequency pulses acrossresistor 46 and stop the S.C.R. 47 turning ON due to momentary operationof one of the transistors 40A, 4013 or 40C. For example, if the switch39 is of the break-before-make type, the transistor -40C will be turnedON for a short period whenever this switch is operated.

It will be seen that the provision of an S.C.R. in place of thetransistor 25 enables an indication of lamp failure to be given afterthe switch controlling nonoperative lamp has opened. The transistor 25may, within the scope of the invention, be replaced by another form oftwo-state device, for example by a bistable.

The electrolytic cell 52 provides, in effect, an integration or summingof the current flow through it. it will be seen, therefore that this maybe replaced by any other device performing a similar integratingfunction, e.g. an accumulator or even a suitably connected pulse circuitdriving a counter.

The circuits described may, in a road vehicle application, include aZener diode shunted across the lines 11 and 12 to absorb voltage spikescaused, for example, by ignition surges. Again, the circuit may be usedto monitor an a-c driven lamp or lamps provided suitable half-orfull-wave rectification is effected. A common feature of all theabove-described preferred embodiment is their suitability formanufacture by integrated circuit technology, and their adaptability forincorporation into the complete circuitry ofa motor vehicle electricalsystem.

it will be further appreciated that the invention is not limited tocircuits monitoring the operation of one or two lamps only, but that bysuitable connections any number of lamps may be checked. Also theindication of lamp failure may not be of necessity given visually, butmay, for example, be given audibly, by operation of a hooter, bell orbuzzer.

Finally, it will be understood that the above description with referenceto the drawings has been given under the assumption that the roadvehicle wiring is of the negative-earth" type. However, if insteadpositive-earth wiring is used, then the circuitry must be suitablyadapted, inter alia by replacing p-n-p transis tors by n-p-n transistorsand vice versa, and the accompanying claims should be so interpreted.

We claim as our invention:

1. An electrical circuit for mobile vehicles to monitor any of aplurality of lamps, said circuit including: a resistive elementconnected in series with each of said lamps, a normally non-conductivetransistor means connected to the junction of each of said lamps and itsassociated resistive element to be biased conductive by the failuresignal potential developed at such junction when that lamp fails,biasing means for said transistor means including at least one diode,said biasing means connected to said transistor means for setting thepotential drop between the base and the emitter of said transistormeans, said bias being substantially insensitive to temperaturevariations, a normally nonconductive semiconductor switch means arrangedto be biased conductive whenever the transistor means conducts, ANDcircuit means coupled to said transistor means for determining actuationof said switch means by said lamp failure signals, and an electricalindicating device connected to be operated by said switch means when thetransistor means conducts.

2. An electrical circuit as claimed in claim 1 wherein the transistormeans is a single multi-emitter transistor having each of the emittersindividually and directly connected to a different one of the junctionsof said lamps and individually associated resistive elements,

and said AND circuit means includes said emitters.

3. An electrical circuit as claimed in claim 1 wherein the transistormeans includes a plurality of p-n-p transistors, the emitter terminal ofeach of said transistors connected to a different one of the junctionsof said lamps and individually associated resistive elements, and asupply line, the collector of each of said transistors connected to saidsupply line.

4. An electrical circuit as claimed in claim 1 wherein a pair of seriesconnected resistors is connected between the collector of the transistormeans and a supply line, the junction of the said resistors connected tobias said semiconductor switch means.

5. An electrical circuit as claimed in claim 1 wherein thesemi-conductor switch means comprises a n-p-n transistor, the collectorcircuit of said n-p-n transistor including said indicating device andthe base-emitter junction of the n-p-n transistor connected across atleast one resistor, whereby in use the potential developed across theresistor when the transistor means is conductive biases the n-p-ntransistor ON.

6. An electrical circuit as claimed in claim 1 wherein the secondsemiconductor switch means comprises a switching device operable ineither a conductive or a non conductive state, and wherein the device isin use operated to change from a non-conductive to a conductive state bythe potential appearing across a resistor whenever the transistor meansconducts.

7. An electrical circuit as claimed in claim 6 wherein an integratingdevice is connected to the semiconductor switch means to indicate thelength of time elasped since failure of one of said lamps.

8. An electrical circuit for monitoring and indicating lamp failure inany one or more of a plurality of lamps in mobile vehicles, comprising:a resistive element connected to each of said lamps, a normallynonconducting sensing transistor connected to a different one of thejunctions of each of said lamps and said re- 7 sistive element connectedthereto, first potential divider means connected to and providing thebase potentials of each of the sensing transistors, a first diode and aresistive element constituting said first potential divider means foreach transistor, a second diode connected to the collector of eachtransistor, second potential divider means connected to said seconddiode, a normally non-conducting semiconductor switch means having acontrol terminal and output terminal, the control terminal of saidswitch means connected to said second potential divider means, and awarning/indicating device connected to said output terminal.

9. An electrical circuit as in claim 8 wherein said warning/indicatingdevice includes an electrolytic cell to indicate the period of time saidwarning/indicating device has been actuated.

10. An electrical circuit as in claim 8 wherein said normallynon-conducting semiconductor switch means comprises a silicon-controlledrectifier.

UNfIEDSTATES PATENT OFFICE (ll lR'll FICA'IE 0b (I(.)RRE(1TION November20, 1973 1. vlnventofls) Wolfgang B1a1 et a It is' certified that errorappears in the above-identified patent and that said Letters Pateht arehereby corrected as shown below:

Cancel the drawings and insert Figures 1 2 and 3 as shown onthe'a tta-ched sheets.

Signed andsealed this 15th day of October 1974.

(SEAL) Attest: V

MCCQY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM P040530 (10-69) USCOMM'DC 60376-P89 U.S GOVERNMiflT PRINTNG DFFICE 8 69- 93 0 Page- 3 Patent-No. 3,774,188

v UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3;774,l88 D d NOVEIHbGT 20,.1973

Inventor(s) f n ial et a1 It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Delete thefigure on the cover sheet and Sheets 1 and 2 of the drawings.I Substitute the attached Figs. 1'- 3.

Patent No. 3,774,188 Page 7 3 NITED STATES PATENT OFFICE I E CATE OFCORRECTION patent 3,774,188 Dated November 20, 1973 Wolfgang Bial et a1.Page 4 Inventor(s) It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

The title of invention should read ELECTRICAL BULB FAILURE INDICATINGCIRCUITS Column 1, after 21, insert the following paragraph:

mMore particularly, in accordance with the invention, an electricalcircuit for mobile vehicles is provided for monitoring any one of aplurality of lamps, andthe circuit includes a resistive elementconnected in series with each lamp and a normally nonconductivetransistor means connected to the junction of each lamp and itsassociated resistive element,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,774,188 Dated November 20, 1973 Inventor(s) Wolfgang Bial et al. Page 5 Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below.

to be biased condu ctive upon the failure ofan associated lamp. Thebiasing means for the transistor means includes at least one diode, andthe biasing means is connected to the transistor means to set thepotentialdrop between the base and emitter of the transistor means, thebias being substantially selfcompensating ror temperature variations Anormally nori-conductiQe switch means is arranged to be biasedconductive when the transistor means conducts, and OR circuit means iscoupled to the transistor means to determine actuation of the switchmeans upon failure of a lamp. Electrical indicating means is connectedto be operated by said switch means when the transistor meansconducts.--

Patent No. 357741188 Dated November 1973 Wolfgang Biel et al. Page 6Inventor(s) It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 4'7, "AND" should read OR Column 3,

line 14, "AND" should read OR Co1umn 4,'lines 30 and 31 "insensitive to"should read self-compensating for lines 34 and 44 "AND", eachoccurrence, should read 7 OR line 55, after "resistors" insert qbeingline 55, delete. "bias". Column 5, line 7, "elasped" should read elapsedSigned and sealed this 4th day of February 1975.

(SEAL) Attest:

McCOY n. mason JR. 0. MARSHALLJDANN Attestlng Officer 7 Commissioner ofPatents

1. An electrical circuit for mobile vehicles to monitor any of aplurality of lamps, said circuit including: a resistive elementconnected in series with each of said lamps, a normally nonconductivetransistor means connected to the junction of each of said lamps and itsassociated resistive element to be biased conductive by the failuresignal potential developed at such junction when that lamp fails,biasing means for said transistor means including at least one diode,said biasing means connected to said transistor means for setting thepotential drop between the base and the emitter of said transistormeans, said bias being substantially insensitive to temperaturevariations, a normally non-conductive semiconductor switch meansarranged to be biased conductive whenever the transistor means conducts,AND circuit means coupled to said transistor means for determiningactuation of said switch means by said lamp failure signals, and anelectrical indicating device connected to be operated by said switchmeans when the transistor means conducts.
 2. An electrical circuit asclaimed in claim 1 wherein the transistor means is a singlemulti-emitter transistor having each of the emitters individually anddirectly connected to a different one of the junctions of said lamps andindividually associated resistive elements, and said AND circuit meansincludes said emitters.
 3. An electrical circuit as claimed in claim 1wherein the transistor means includes a plurality of p-n-p transistors,the emitter terminal of each of said transistors connected to adifferent one of the junctions of said lamps and individually associatedresistive elements, and a supply line, the collector of each of saidtransistors connected to said supply line.
 4. An electrical circuit asclaimed in claim 1 wherein a pair of series connected resistors isconnected between the collector of the transistor means and a supplyline, the junction of the said resistors connected to bias saidsemiconductor switch means.
 5. An electrical circuit as claimed in claim1 wherein the semi-conductor switch means comprises a n-p-n transistor,the collector circuit of said n-p-n transistor including said indicatingdevice and the base-emitter junction of the n-p-n transistor connectedacross at least one resistor, whereby in use the potential developedacross the resistor when the transistor means is conductive biases then-p-n transistor ON.
 6. An electrical circuit as claimed in claim 1wherein the second semiconductor switch means comprises a switchingdevice operable in either a conductive or a non-conductive state, andwherein the device is in use operated to change from a non-conductive toa conductive state by the potential appearing across a resistor wheneverthe transistor means conducts.
 7. An electrical circuit as claimed inclaim 6 wherein an integrating device is connected to the semiconductorswitch means to indicate the length of time elasped since failure of oneof said lamps.
 8. An electrical circuit for monitoring and indicatinglamp failure in any one or more of a plurality of lamps in mobilevehicles, comprising: a resistive element connected to each of saidlamps, a normally non-conducting sensing transistor connected to adifferent one of the junctions of each of said lamps and said resistiveelement connected thereto, first potential divider means connected toand providing the base potentials of each of the sensing transistors, afirst diode and a resistive element constituting said first potentialdivider means for each transistor, a second diode connected to thecollector of each transistor, second potential divider meaNs connectedto said second diode, a normally non-conducting semiconductor switchmeans having a control terminal and output terminal, the controlterminal of said switch means connected to said second potential dividermeans, and a warning/indicating device connected to said outputterminal.
 9. An electrical circuit as in claim 8 wherein saidwarning/indicating device includes an electrolytic cell to indicate theperiod of time said warning/indicating device has been actuated.
 10. Anelectrical circuit as in claim 8 wherein said normally non-conductingsemiconductor switch means comprises a silicon-controlled rectifier.